Monday, November 8, 2010

Sights: Telescopic Sight - I

In the last few posts, we covered a lot of details about different types of iron sights. In the next series of posts, we will cover another type of sight, the telescopic sight.

One feature in common among different types of iron sights that we studied previously is that they do not perform any image magnification. Hence, if the user has bad eyesight or if the target is somewhat further away, they are less effective. The telescopic sight attempts to solve this problem.

The first telescope was invented by a German-Dutchman named Hans Lippershey in Netherlands in 1608. Later improvements were made by other users, including the famous Italian scientist, Galileo Galilei. Soon after this, telescopes were quickly co-opted for use in warfare, for tasks such as observing enemy formations, determining where artillery shells are falling, observing enemy ships etc. It is, therefore, very surprising to discover that telescopic sights weren't used in firearms for a very long time. In fact, the first mention of a telescope in a firearms sight occurred around 1835-1840, which is almost 230 years after the telescope was invented!

The first mention of telescopic sights was by John Chapman in the book The Improved American Rifle, published in 1844. The author mentions that he was a civil engineer by training and had given Morgan James of Utica, NY, the concepts and part of the design of a sight that James had built for him. The Chapman-James sight was the first known telescopic sight designed for firearms. Later improvements were made in 1855 by one William Malcolm of Syracuse, NY, who learned how to make telescopes from a telescope maker. Such sights were in use during the American Civil War. The first telescopic sight that actually worked well for practical use, was invented in 1880 by one August Fiedler from the town of Stronsdorf, Austria, who worked as a forestry commissioner of Prince Reuss. There were other improvements made by various parties and soon, an Austrian firm named Kahles started factory production, thereby becoming the oldest known manufacturer of rifle scopes. So it was close to the 1900s that the popularity of telescopic sights really started. The Kahles Company is still around as a division of the Swarovski group (the same people known for making Swarovski crystal jewelry and chandeliers) and still making quality rifle scopes.

Public domain image. Click to enlarge.

Telescopic sights are of two types: (a) fixed magnification and (b) variable magnification. Variable magnification scopes can change their magnification via a zoom control and can therefore adjust to varying ranges and light conditions.

Telescopic sights usually have reticles to make aiming more precise. The image below shows various types of reticles:

Public domain image. Click image to enlarge.

The classic reticle one sees in movies is generally the Fine Crosshair type shown above. It must be noted that while fine lines are suitable for precision aiming, they generally tend to get lost in complex backgrounds. Thicker lines are more visible against noisy backgrounds, but they lose some of the precision. Hence, modern scopes use a mixture of both, (i.e.) thicker lines towards the outside and thin lines towards the center of the scope. Example of this would be the Duplex Crosshair, the Mil-Dot and Modern Rangefinding reticles in the image above.

Most modern scopes also have ways to determine the distance to the target, so that the rifle may be suitably adjusted for elevation and windage. This is done by making a series of graduated markings on the reticles, as seen in the Mil-Dot, Modern Rangefinding and SVD Type reticle images above. Note: The SVD type reticle was originally designed for the Soviet Dragunov SVD sniper rifle. Some more examples of such markings are shown below.

Above image is licensed under GNU Free Documentation License 1.2 by Kosiarz-PL at
Public domain image of Schmidt & Bender scope reticle

Such markings make it easy to estimate the range of a target if its height or width are roughly known in advance. For example, in the Schmidt & Bender scope, which is used by Dutch snipers, an object that is 1 meter tall or 1 meter wide at a distance of 1000 meters will appear to be exactly the width or height between two of the dots in the reticle image above. Therefore, the distance to a target is determined by the formula:
distance in meters = (known height or width of target / number of dots) * 1000

So, say the user is aiming the scope at a human target. Say that the human target stands about 3 dots tall, when viewed through the scope. Assuming that an average human is about 1.8 meters tall, then distance to the human target is estimated as (1.8 / 3) * 1000 = 600 meters.

Now, by knowing the distance to the target and knowing how his rifle performs at various distances, the user can adjust the elevation and windage of the weapon accordingly.

There is also an even quicker way to estimate distance, which does not involve any arithmetic. Notice that in the lower half of the reticle of the Schmidt & Bender scope image above, there is a horizontal line and above it are a series of shorter horizontal lines in a step formation. These lines can also be used to determine distance by using a human target as the scale, without doing any mental arithmetic. To estimate distances from 100-250 meters, the user merely frames the target's head between the horizontal lines as shown in the image below. The average human's head with helmet is approximately 0.25 meters high. When viewed through the scope, the two lines that best frame the target's head tells the user the approximate distance to the target.

Public domain image

To tell distances between 400 - 1000 meters, the user frames the target's upper body (i.e. the area between the head and belt-buckle) between the same horizontal lines and estimates the distance as follows:

Public domain image

Similarly, for the other range finding scope, it may be aimed at a target of known width, such as a tank, and the range may be easily looked up:

From the image above, one may say that the tank is roughly about 275 meters away.

Well that's a lot to absorb in one post. We will continue to discuss more about telescopic sights in the next post as well.

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